Teletypewriter switching system



vM313' 23, 1944. c. A. DAHLBOM Erm. 2,349,539

TELETYPEWRITER SWITCHING SYSTEM Filed Dee. 2e, 1941 '7 sheets-sheet A1 y no w 0 R ad... o ...x r wie r ANO A L DMA. As an@ wwf w 0 W V B w. W

May 23,1944# c. A. DAHLBoM ETAL' 2,349,539

TELETYPEWRITER SWITCHING SYSTEM l Filed Dm. 2e, 141 'fsheet-sneet 2 C A. DAHLBOM INVENTORS! FI S. KIN/(EAD ATTORNEY May 23, 1944. c. A. DAHLBOM ETAL 2,349,539

TELETYPEWRITEB SWITCHING SYSTEM Filed Dec. 26, 1941 '7 Sheets-*Sheet 5 SUE RING

ANS.

MODEL 33 RE CALL ATTORNEY May 23, 1944- Y y c. A. DAHLBOM ETA; y 2,349,539

TELETYPEWRITER SWI'TCHING SYSTEM Filed Dec. 2e, 1941 7 sheets-sheet` 4 l a I' l l m e.

l ATTORNEY May 23,1944. c. A DAHLBoM Erm.

I TELETYPEWRITR SWITCHING SYSTEM Filed Dec. ze, 1941 #sheets-sheet 5 May 23, 1944- c. A. DAHLBoM Erm. 2,349,539

TELETYPEWRITER SWITCHING SYS TEM A7' TORNE Y ward service.

Patented May 23, 1944- UNITED STATES PATENT OFFICE TELETYPEWRITER sWITcHING SYSTEM Carl A. Dahlbom, Brooklyn, Fullerton S. Kinkead, New York, and George A. Locke, Glenwood Landing, N. Y., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 26, 1941, Serial No. 424,436

(o1. iis- 2) 29 Claims.

This invention relates to manual teletypewriter `switching systems. An object of the invention is to provide improved manual straightforward teletypewriter switching circuits. A feature of the 4invention is a group of cooperating teletypewriter;

switching circuits arranged to provide what is known in the art as automatic through and in- "It is desirable, in the operation of manual teletypewriter switching systems, in cases Where calls are extended through more than one central switching station, that an operator at one of the central switching stations only should control the call. It is preferable vthat the operator at the switchboard where'the call originates should con.. trol the call. In order to do this, switching information governing the progress of the call through succeeding central stations and the connection of the` call ultimately to the called subscriber should be transmitted from the originati ving ofce by the originating central station operator. It is preferable also that means for ringing lthe called subscriber should be under control of the operator at the originating station. Disconnect signals should be registered also at the originating oice in response to disconnection by the subscriber without the necessity for intervention `by any of theA operators at the other central stations through which a toll call may pass in tandem. It is preferable also that recall signals be recorded at the originating oiiice. Reference is made to F. J. Singer Patent 2,228,890, issued J anuary 14, 1941, which discloses a manual straightforward teletypewriter switching system.

An object of theinvention described herein is to, provide features of operation, which, in certain respects are improvements over those disclosed in Patent 2,228,890.

Among these improvements is more positive control of a supervisory relay and attendant modifications whereby the full operatingr advantage of such more positive control is obtained.

The nature of these improvements will become more apparent in the following description and will be particularly pointed out in the appended claims.

In the drawings:

Fig. l shows a subscribers station circuit, chown at the left or" the iigure, which is connected by two conductors to a station line terminating circuit, shown at the right ci the figure located at a teletypewriter central switching station to be known as oflice I;

. Fig. 2 shows a teletypewriter cord Circuit which is assumed to be located at office I for use in establishing connections at the central station;

Fig. 3 represents an operators position circuit which cooperates with the cord circuit per Fig. 2 to provide means so that the central station operator at oflice l may communicate by means of a teletypewriter to circuits connected to either end of the cord. Fig. 3 includes also means for transmitting supervisory signals through the cord;

Fig. 4 is an automatic intertoll terminating circuit located at oiiice I;

Fig. 5 is a telegraph repeater circuit located also at oice I, to which Fig. 4 connects:

Fig.v 6 Ais a telegraph repeater circuit identical with Fig. 5, except that it is shown in reverse, located at a secondy centralI switching ofiice to be known as oflice 2, to which the outgoing end of the repeater per Fig. 5 is connected by means of conductors interconnecting cnice I and oce 2;

Fig. '7 is an automatic intertoll trunk terminating circuit identical with Fig. 4, except that it is shown in reverse, located at oiTice 2, to which the incoming end of the repeater circuit per Fig. 6 at oice 2 is connected;

Figs. 4, 5, 6 and 7 when connected together in numerical sequence constitute an automatic intertoll trunk circuit interconnecting two central teletypewriter- Switching ofces, oice I and ofiice 2;

Fig. 8 is a station line circuit and subscribers station circuit which is identical electrically with Fig. 1 except that it s shown in reverse. It is assumed to be connected to ofce 2; and

Fig. 9 is a diagram which shows the manner in which Figs. l to 8 herein are arranged in relation, each to the other, in order to conform to the accompanying text.

As shown in Fig. 9, a subscriber-s station A, shown at the left of Fig. 1, is connected by means of two conductors to a station line circuit at a rst central switching station. The station line circuit is terminated at the central station in multiple jacks and lamps as indicated in Fig. l of which only one jack is indicated in Fig. 9. I1; is pointed out that many subscribers station circuits and station line circuits, such as Fig. 1, will be connected to the switchboard at the first central station. Fig. 2 represents a cord circuit. The cor-d circuit has two ends terminated in plugs called answering and calling plugs. The answering plug, indicated at the left, is used in answering an incoming call. The calling plug, indicated at the right, is used in extending a call which has been answered. Ordinarily, there are about fteen cord circuits such as Fig. 2 located a1; a

particular position. Any one of the cord circuits may be used on a particular call. An opcrators position circuit per Fig. 3 is shown connected to the cord circuit. Although there may be approximately fifteen cords such as Fig. 2 at a particular position, there is only one operators position circuit at each position. The circuits are arranged so that the operators position circuit may be oonnected temporarily to the cord circuit per Fig'. 2 While switching information is obtained and it may remain connected to the cord until the call is established. Thereafter the operators position circuit per Fig. 3 is disconnected from the cord so as to be available for connection .to other cords.

The rst central station oflice I and the succeedi ing central station oice 2 in a tandem connection are interconnected by means of Fig. Ll, Fig. 5, Fig. 6 and Fig. '7. Figs. 4 and 5 are assumed t be locate-d at the rst central station. Fig. 5 at the first central station is connected to Fig. 6 at the second central station by means of two conductors indicated by the dotted line. The trunk circuit incoming to the second central sta.- tion passes through the repeater per Fig. 6 which is identical with the repeater per Fig. and then through the relay equipment of the automatic intertoll trunk terminating circuit per Fig. Y?. It is pointed out that Fig. 5 and Fig. 6 provide for half duplex operation between oiiices. rihe repeaters shown in these ngures may be replaced by full duplex repeaters in which case only one conductor interconnecting ofii'ce I and oice 2 would be required. It is terminated in a jack indicated at the right of Fig. '7 in switchboard at the second central switching station oiiice 2. A cord circuit identical with Fig. 2 and an operators position circuit identical with Fig. 3 are shown at the second central switching station.

`The cord. circuit at oiiice 2, shown in Fig. 9, and

manner in which it may be performed may be understood from the description herein, as the trunk, cord and position circuits will operate in the same manner on successive connections to other oiicesas described herein.

The cord circuit per Fig. 2 and the operators position circuit per Fig. 3 `may be used with trunk circuits other than those disclosed herein. The trunk circuit disclosed herein is an automatic signaling intertoll trunk. Figs. 2 and 3 will function also with ringdown trunks. Although the ringdown trunks per se are not described in this application, the manner in which certain supervisory and ringing signals maybe transmitted by the operators position circuit when it cooperates also with ringdown trunks is described `herein.

Subscriber originates call The manner in which the subscriber at station A calls the central station will now be described.

The circuit per Fig. 1 is shown as arranged in its idle condition. For this condition a circuit may be traced from ground at the central station through resistance |93, through relay contact IMb, relay contact Ia, resistance Hi8, conductor IBI, key contacts IUIb and Il'Id to ground. Both ends of conductor ISI are grounded, it may be observed, while the circuit per Fig. l is idle. A circuit may also be traced from positive battery through resistance |98, relay contact Ie, top Winding of relay |89, resistance Iii), conductor |62 and resistance Iil to terminal H2. At terminal ||2 parallel branches are formed. One branch extends to key contact Iic which is open. The other branch extends through condenser ||3 and ringer H4 to terminal IE5. From terminal H5 parallel branches extend. Gne branch extends through key contacts i'ib and IUICZ to direct ground. This branch short-circuits the branch extending through break key IZ'I teletypewriter receiving magnet |23 and teletypewriter transmitting contacts IIt which also extends to ground through key contacts 1Mb iil'ld. Since one branch extending from terminal ||2 is open at contact llc and the other branch extends through a condenser I I3, no current will flow through conductor i532 from the direct current source connected to resistance |68 While the circuit per Fig. 1 is idle.

1n order to initiate a call the subscriber at station A operates key IB? to its alternate position. This closes contact Itlla. This establishes a circuit irom a source of alternating current ||1 through teletypewriter motor IIS and key contact ima to the opposite side of power source lii'i starting the motor. The operation of key HB1 also opens contacts IU'Ib and ID'Id. This removes direct ground from conductor IUI and also removes ground from the ringer circuit. Conductors iii! and |32 are interconnected over a circuit which extends from terminal II'2 through key contact Iil'lc, teletypewriter transmitting contacts IIS, teletypewriter receiving magnet |23, break key |21 and terminal ||5 to conductor IUI. When conductors IGI and |02 .are interconnected through the teletypewriter circuit the circuit from battery through resistance H36 is completed to ground through resistance Ii. 'I'his energizes the top winding of relay |99, operating relay |09. The operation of relay Iiiiestablishes a circuit from ground through contact 209e, winding of relay 04, contact IDEC and resistance i E9 to battery operating relay |04. The operation of relay |64 establishes a circuit from battery through contact ilid. and the filament of lamp |20 to ground lighting lamp |20 as a signal that the subscriber at station A is calling. The operation of relay |04 also disconnects ground through resistance |03 and contacts Idb from conductor Iiii and replaces it by negative telegraph battery through resistances IZI and |22 and contact Ia. The operation of relay IEM also connects ground to the night alarm circuit through contact !!Mc. With negative battery connected to conductor IGI and positive battery connected to conductor HB2 full marking current i'iows around the subscribers loop circuit and through the winding of receiving magnet |23. This current in the receiving magnet |23 maintains the subscribers teletypewriter marking condition.

Answering incoming call from subscriber Zine A line signal indicating that a call is incoming from a subscribers line is answered by inserting the answering plug Ztl of Fig. 2 into jack |24 of Fig. 1 associated with the calling line. The sleeve conductor of the answering plug 20| in Fig. 2 is connected to ground through the winding of relay |35 in the sleeve circuit roi the calling line per Fig. 1 and the circuit extends from the sleeve, or bottom conductor, of plug 20|, through contacts 2081), left-hand winding of relay 205 and the winding of relay 204 to battery. Relay |05 in Fig. 1 and relays 205 and 204 in the cord circuit per Fig. 2 operate.

The operation of relay |05 opens contacts |05c, disconnecting battery from the winding of relay |04. Relay |04 releases. The release of relay |04 opens contact |04d extinguishing lamp |20. The release of relay |04 opens Contact |04c disconnecting the night alarm circuit. The release of relay |04 opens contact |04a disconnecting negative battery through resistances |2| and |22 from conductor |0I. Contact |0417 is reclosed connecting ground through resistance |03 through contact |041), but this performs no function at this time as relay |05 is operated.

The operation of relay |05, by opening contact |0511, transfers conductor from the path to negative battery through Contact |04a and connects it instead to negative battery through the bottom winding of relay |09 and resistance |2I. The opening of contact |05e disconnects positive battery through `resistance |08 from conductor |02 and extends conductor |02 through contact |05d to the tip or top conductor of jack |24.

Attention is called to the fact that conductor |0| is terminated in negative battery through the bottom winding of relay |09. Conductor |02 extends through the top winding of relay |09 and contact |05d to the tip conductor of jack |24. The tip circuit in the cord extends to positive battery, as will be seen when that circuit is subsequently traced. The effects of the current in the top and bottom windings of relay |09 for this condition are equal and opposed. Relay |09 releases. Contact |09a opens. The ring or middle conductor of jack |24 is open therefore for this condition as both contacts |051: and-contacts |09a are open.

In Fig. 2 the operation of relay 204 establishes a circuit from ground through contact 204D and the winding of relay 2|3 to battery operating relay 2|3. The operation of relay 2 I3 opens conf tact 2|3b which when closed provides a path for the operation of a busy test and cord interference signal in the operators position circuit per Fig. 3, to be described below. graph transmission path for the answering end of the cord at contact 2|3c. The operation of relay 2|3 also operates relay 22| from battery through contact 2|3a, resistance 24'` and the leithand winding of relay 22| to ground. The operation of relay 22| closes ground to the articial line circuits of repeater relays 222 and 223. The operation of relay 22| also provides holding battery for the line windings of relays 222 and 223, when required, to hold the armatures of these relays on their marking contact. This will now be described in more detail.

Relays 222 and 223 are shown with their armatures in engagement with their spacing contacts. Before plug is inserted in jack |24 and before relay 22| is operated, no current flows through any of the windings of relay 222 and 223. When plug 20| is inserted into jack |24 the tip of plug 20| is connected to the tip of the associated sub scribers line circuit. When the subscribers line circuit is closed for the marking condition` a loop is established through the line circuit and the return loop conductor is terminated in Fig. .1 in negative battery connected to resistance |2|. From the tip of plug 20| the circuit extends through contact 2|3d, resistance 239, contacts It also closes the telel 2| 9a. and 2|9e in parallel, contacts 220D and 220e in parallel and the bottom winding of relay 222 to the armature of relay 223. When the armature of relay 223 is in engagement with its spacing contact 223s, as shown, the circuit extends through resistance 253 to negative battery. Since both ends of the loop are terminated in battery of the same magnitude and polarity for this condition, no current flows in the loop and the bottom Winding of relay 222 is deenergized. With relay 22| operated a circuit may be traced from ground through Contact 22 la, resistance 244, top Winding of relay 222, armature of relay 223, contacts 223s and resistance 253 to negative battery. The current iiowing in this path energizes the top winding of relay 222 and its effect actuates the armature of relay 222 to engage with its marking contact 222m. The operation of relay 22| also provides a path from negative battery through resistance 249, Contact 22|d, resistance 242, contact 2|1c, contact 2|8a, resistance 243 and the bottom winding of relay 223 to the armature of relay 222. When the armature is in engagement with its marking contact 222m, the circuit is' extended through resistance 250 to positive battery. It will be observedthat the opposite ends of this path are terminated in batteries of opposite polarity so that the batteries are in series-aiding relationship. Full line current, therefore, flows through the bottom winding of relay 223. A circuit may also be traced from ground through contact 22|b, resistance 245and the top winding of relay 223 to the armature of relay 222. When the armature of relay 222 is in engagement with its right-hand or marking contact 222m, the circuit extends through resistance 250 to positive battery. The eiect of current owing in the bottom or line winding of relay 223 tends tov actuate the armature of relay 223 to engage with its lefthand or marking contact. This eiect is opposed by the effect of current flowing through the top winding of relay 223 which eiect is tending to actuate the armature of relay 223 to engage with its right-hand or spacing contact 223s. The effect of the current in the bottom or line winding of relay 223 preponderates for this condition and the armature of relay 223 is actuatedso as to engage with its left-hand or marking contact 223m. When the armature of relay 223- engages with marking contact 223m, the subscribers loop is terminated in the circuit extending through resistance 25| to positive battery. For the marking condition, therefore, when the subscribers loop circuit is closed, conductor |0| is permanently terminated in negative battery through resistance |2| and conductor |02 is extended through the transmission conductor of the answering side of the cord and is terminated in positive battery through resistance 25 The telegraph signaling batteries at each end of this transmission path, therefore, are in series-aiding relationship for the marking condition. Full line current, therefore, flows through the bottom or line winding of relay 222 and telegraph receiving magnet |23 for the marking condition. The effect of this current in relay 222 will maintain the armature of relay 222 in engagement with its right-hand or marking contact 222m. The direction of current flow through the top winding of relay 222 is reversed when the armature of relay 223 engages with its marking contact. The effect of current in the top winding of relay 222 for this condition tends to actuate the armature of relay 222 towards its left-hand or spacing contact 222s,

but it is ineffectual, since the eifect of current in the bottom or line winding of relay 222 is dominant and the armature of relay 222 is maintained in engagement with its right-hand or marking contact 222m. When the armature of relay 222 is in engagement with its right-hand or marking contact 222m.J the direction of the flow of current through the top winding of relay 223 is reversed. This tends to actuate the armature of relay 223 to engage with its spacing Contact 223s, but the e`ect of current in the bottom or line winding of relay 223s, tending to actuate the armature of relay 223 towards contact 223m, is dominant and the armature of relay 223 is maintained in engagement with its left-hand or marking contact 223m.

In tracing the sleeve circuit in the cord, it was shown to extend through the left-hand winding of relay 225 and the winding of relay 224 to negative battery. This is a high resistance path. After relay 225 has been operated, a parallel low resistance looking path for relay 235 is established extending through the right-hand winding of rey lay 205 and resistance 233 to negative battery. The object of this is to establish a low resistance sleeve circuit to provide protection against interference caused by the connection of more than one cord circuit simultaneously tothe same line circuit. This will now be described in more detail.

Prevention of interference when rmore than one cord is connected simultaneously to one Zine The manner in which interference is prevented when in response to the simultaneous lighting of a number of line lamps, such as and |26 at different operators positions, more than one cord circuit,fsuch as the cord per Fig. 2 herein, are connected through multiple jacks such as jacks |24 and |25, simultaneously to the same line circuit, such as Fig. l, will now be described.

If a second cord circuit, such as Fig. 2 is plugged into one oi' the multiple appearances of jack |24 such as jack 225, while one cord per Fig. 2 is already connected to jack 2.1i, the relay corresponding to relay 25.32 in the second or interfering Cord will operate, but the relay in the interfering cord corresponding to relay 205, which is a marginal relay, will not operate, owing to the shunting effeet of the low resistance sleeve circuit through thelright-hand winding of relay 205, resistance 233 and contact 225e to battery in the first cord. Relay of the interfering cord, when operated,.operates relay 253 of the interfering cord inthe same manner as described above. The operation of relay Zilli in the interfering cord also -operates relay in the interfering cord, over a lcircuit corresponding to that which may be traced from ground thro-ugh contact 22Std, winding of relay 223 and contact 225k to battery. As explained above, the relay corresponding to relay 225 in the interieringv Cord is not operated, and therefore the path through contact 2251 is available for operating the relay corresponding to relay 263 in the interfering cord.

The operation of relay 2|@ in the interfering cord closes the transmission path in the interfering cord through contact 2l2d. It also operates relay 22| in the interfering cord. The corresponding path has heretofore been traced. This energizes'the biasing windings of the polar repeater relays corresponding to relays 222 and 223 in the interfering cord. It also supplies negative battery to the right-hand terminal of the bottom or line Winding of the relay corresponding to relay 223 in the interfering cord. In the interfering cord the operation of relay 223 establishes a circuit which may be traced from positive battery through resistance 25|, contact 203e, resistance 239, contacts 2|9a and 2|9e in parallel, contacts 22217 and 222e in parallel and the bottom or line winding of relay 222 to the armature of relay 223. For this condition the armature of the polar relay in the interfering cord corresponding to relay 223 will be actuated so as to engage with its marking contact. The armature of the relay corresponding to relay 222 in the interfering cord will be actuated so as to engage with its spacing contact. This prevents transmission through the interfering cord. This will now be explained in detail.

The explanation of this is as follows. Positive potential through resistance 25| and Contact 203e has been connected to the left-hand terminal of the bottom winding of relay 222. Ordinarily as described above for the normal condition, with one cord circuit connected to one line jack, when the line circuit, per Fig. l, is closed, negative battery through resistance |2| in Fig. l is connected to the left-hand terminal of relay 222. If the armature of relay 223 is in engagement with its left-hand or marking contact under such condition, positive battery through resistance 25| is connected through contacts 223s to the righthand terminal of relay 222. For the normal `marking condition therefore the full line current flows through the bottom winding of relay 222 in a direction to actuate the armature of relay 222 to the right to engage its marking Contact 222m. The effect of the current in the biasing winding of relay 222 opposes this and tends to actuate the armature of relay 222 toward the left, to engage its spacing `contact 222s, but the effect in the bottom winding is dominant and the armature of relay 222 engages Contact 222m.

When, lfor the cord interfering condition, positive battery is connected through resistance 25| and contact 283e to the left-hand terminal of the bottom winding of relay 222, if the armature of relay 22S is in engagement with its spacing contact 223s, negative battery through resistance 253 and contact 223s is connected to the righthand terminal of the bottom winding of relay 222. Full line current flows through the bottom winding of relay 222, but its direction is now reversed from its direction for the normal marking condition and the armature of relay 222 for this condition will be actuated to engage with its left-hand or spacing contact 222s. The effect of the current flowing through the top or biasing winding of relay 222 for this condition would tend to actuate the armature of relay 222 to its marking Contact, but the effect in the bottom winding of relay 222 wo-uld be dominant. Thus for thecord interfering condition if the armature of relay 223 is in engagement with its spacing contact the armature of relay 222 will be actuated to engage with its contact 222s.

Let it be assumed that the cord interfering condition prevails, but that the armature of relay 223 is in engagement with contact 223m. For this condition positive battery through resistance 25| and contact 20M is connected to the left-hand terminal of the bottom winding of relay 222 and the same battery through resistance 25|, contact 223m and the armature of relay 223 is connected to the right-hand terminal of the bottom winding of relay 222. No current therefore ilows in the bottom Winding of relay 222. The direction of the current owlng in the top winding of relay 222 is reversed as negative battery instead of positive battery is connected to ground through the top Winding of relay 222. Now, therefore, the eiect of the biasing current in the top Winding of relay 222 prevails and the armature of relay 222 is actuated to engage with its spacing contact 222s.

So, no matter on Which contact the armature of relay 223 may be, the armature of relay 222 is actuated to engage contact 222s for the cord interfering condition.

Therefore, for the cord interfering condition, negative battery will be connected through contact 222s to the left-hand terminal of the bottom Winding of relay 223. The right-hand terminal of the bottom Winding of relay 223 has been shown to be connected through resistance 243, contact 2|8a, contact 2|'|c, resistance 242, contact 22|d and resistance 249 to negative battery. No current, therefore, flows in the bottom Winding of relay 223. With the armature of relay 222 on contact 222s, the left-hand terminal of the top Winding of relay 223 is connected to negative battery. The right-hand terminal, as has been shown, connects to ground through resistance 245 and contact 22|b. Since positive battery connected to the left-hand terminal of relay 223 tends to actuate its armature toward contact 223s, unopposed negative battery connected to the left-hand terminal of the bottom winding of relay 223 will operate its armature to contact 223m where it, during the cord interfering condition, Will be maintained.

Thus, in the interfering cord, relay 222 will be maintained in a spacing condition and relay 223 will be maintained in the marking condition Whenever there is an interfering cord condition. This prevents transmission through the cord.

While this condition persists the subscribers line circuit per Fig. 1 Will be held in the marking condition as positive battery Will continue to be impressed on the tip conductor of the subscribers line `jack over parallel paths. One path is through resistance 253, contact 223s and the tip transmission conductor to the tip of plug The other path is through resistance contact 203a, resistance 239, contact 2|3d to the tip of plug 20|.

In the operators position circuit associated with the interfering cord, a signal is` provided to indicate the interfering condition in the following manner. In the interfering cord the operation of key 224 or key 225 will operate relay 2|9 or relay 220 over obvious circuits. This connects the operators position circuit at the home or adjacent position to the interfering cord depending upon vvhich key is operated. A circuit is then established from negative battery through resistance 232, contact 20319, and contact 2|9g or contact 220g depending upon which key is operated. The armature associated with each of these contacts is connected to a relay in its associated operators position circuit Which lights a lamp, to indicate the interfering condition. The circuit will be traced hereinafter. Upon observing this the interfering operator will disconnect the interfering cord.

During the interval while the interfering cord Was connected, the positive battery, supplied from the interfering cord through resistance 25| and contact 203a to the tip transmission conductor, to operate the armature of polar relay 222 in the interfering cord to spacing and prevent transmission through the interfering cord, was impressed also through contact 2|3d of the interfering cord, relay 2|3 being operated, on the tip of the plug such as 20| of the interfering cord. The tip of the interfering cord is connected to thevtip of one of the subscribers line jacks, such as jack |25. The subscribers line jacks of a particular line are all connected in multiple as shown in Fig. 1. The tip of the original cord is therefore connected in parallel with the tip of the interfering cord. As a result of this the armature of polar relay 222 of the original cord is also actuated to its spacing contact and maintained thereon as long as the interfering cord remains connected. The battery conditions in the windings of the polar repeating relays 222 and 223 and their effects are the same in the original cord as described above for the interfering cord. Thus transmission through either cord is prevented While the interfering condition persists.

When the interfering cord is removed and the actuated typing key therein is restored to normal the relays in the interfering cord are all restored to normal. The armature of polar relay 222 of the original cord is returned to its marking contact and transmission through the original cord may be resumed.

Connection to operators position circuit As mentioned above, a number of the cord circuits herein, such as fteen, may be located at a particular operators position in a switchboard. The position is provided also with a single operators position circuit such as Fig. 3. Adjoining positions in the switchboard are similarly equipped with, say fifteen cords and one position circuit. When a particular cord circuit is selected for use, it is necessary to connect a position circuit to that particular cord temporarily, so as to provide means whereby the operator at a particular position may communicate with the subscriber and receive the number of the called party or Whatever direction is to be passed to the operator. After the operator has received this information and performed the necessary switching function or Whatever function may be required, the position circuit is disconnected from the particular cord so as to be available for connection to other cords as required. The circuit herein is arranged in such a manner that it may be connected to a position circuit at the particular position Where the cord circuit is located, or it may be alternatively connected to an operators position circuit at an adjoining position. This feature is provided so that operators at adjoining positions may function as a team during periods of heavy load.

Each cord circuit at a particular position is i provided With tWo keys such as 224 and 225. One

key, key 224, connects the operators position circuit located in the same position at which the cords are located to the particular cord. The other key, key 225, connects the operators position circuit in an adjoining position to the cord circuit. If it is desired to connect the operators position circuit located at the same position as that at which the cord circuit is located to the cord, key 224 is operated. This establishes a circuit from ground through contact 224er, and the Winding of relay 2|9 to battery operating relay 2|9. The operation of relay 2|3 opens the transmission path interconnecting the tip of plug 20| and the bottom Winding of polar relay 222 at two` points, namely, at contacts 2|9a and contacts 2|9e and connects the transmission circuit of the operators position circuit in series between continuity contacts 2|9b and 2|3f. Alternatively the operation of key 225 establishes a circuit from ground through contact 225f and the winding of relay 223 to battery operating relay 223. This inserts the transmission circuit of the operators position circuit at an adjoining position between the tip of plug 20| and the bottom winding of polar relay 222. Contacts 22|lb and 223e in parallel in the transmission path through the answering end of the cord are opened and the transmission circuit through the adjacent operators position circuit is inserted. in series between continuity contacts 22M and 220i. The operation of relays 2|9 and 22) perform other switching functions which will be described hereinafter.

Circuit conditions in cord and line circuits for busy test A busy test is made by touching the tip of either answering plug 210| or calling plug 2||` to the sleeve of a line jack before inserting the plug into the jack in order to guard against double connections. if the circuit associated with the line jack is busy, due to the connection of another cord, such as Fig. 2 to one of the multiple appearances of jack |241, such as jack |25, at another position in the board, negative battery will be connected to the sleeve of the jack from the sleeve of the associated answering or calling plug of the other connected cord.

The circuit may be traced from negative battery over parallel paths. rIhe first path extends through the winding of relay 2M and the lefthand winding of relay 225'. The second path extends through contact 235a, resistance 233 and the right-hand winding of relay 235. The paths join and the circuit continues through contacts 238D and the sleeve of plug 23| to the sleeve of jack |25 which is connected in multiple to the sleeve of jack |24. If, instead of an answering plug, such as 23|, a calling plug, such as 2| of a cord circuit similar to the cord circuit per Fig. 2 herein has already been inserted in one of the multiple appearances of jack |24, negative battery is supplied through the winding of relay 2|1 and resistance 263 in parallel through the sleeve of plug 2|| to the sleeve of the jack to which calling plug 2| |I is connected, which sleeve is also connected in parallel to the sleeve of jack |213. Attention is called to the fact that when the testing is performed by touching the tip of the plug to the sleeve of the jack, the whole plug is not inserted into the jack and the relays controlled by the sleeve circuit of the cord. which is testing will not be operated. Before making a busy test an operator will operate either key 224 or key 225 in the particular cord to its alternate position.

It will be assumed first that the testing is performed by touching the tip of plug 26| to the sleeve of a jack such as |24 on which negative battery has been impressed from another cord. Negative battery on the sleeve of the jack is impressed through the tip of plug 23|, Contact 2|3b` and, if key 224 has been actuated, through contact 2| 9g and over a conductor which extends into the home operators position circuit, through the winding of a relay connected thereto, to light a lamp in the position circuit as an indication of the busy condition. The manner in which lamp in the operators position circuit is lighted will be described in detail below. If key 225 has been operated so that relay 22D, rather than relay 2|9, has been operated, to connect the operators position of the adjacent position to the particular cord, the circuit extends through congsi-tsss tact 223g to corresponding apparatus in the adjacent operators position circuit.

If the calling plug 2| l is to be used in establishing a connection, the busy test will be made by first touching the tip of plug 2|| to the sleeve of the jack. If the jack circuit is already busy, negative battery will be impressed through the tip of plug 21|, contact 2351i of ringing key 235, contact 2i33d, contact 2|1b and through either Contact 2|9g or 223g to light the busy lamp in the position circuit.

operators position circuit As indicated in Fig. 9, Fig. 3 connects to Fig. 2. The leads shown extending to the bottom margin of Fig. 2 connect to conductors in corresponding positions extending to the upper margin of Fig. 3. Thus conductors 21| to 218 in Fig. 2 connect to conductors 31| to 318 in Fig. 3.

For the following description before key 224 is operated to operate relay 2|l and connect the operators position circuit per Fig. 3 of the home position to the cord circuit per Fig. 2 key 328 in Fig. 3 is assumed to be operated, so as to close its contacts 323a, 328D and 3280. The closure of contact 328a establishes a circuit which may be traced from battery through resistance 324, bottom winding of relay 3|8 and key contact 328e, to ground, energizing the bottom winding of relay Siti. The energization of the bottom winding of relay 3|8 actua-tes its armature to engage with its contact 3|3s. The top winding of relay 3| 3 is not energized as the transmission circuit of the operators position circuit per Fig. 3 which extends through the top winding of relay 3|8 is open at relay contacts 2|9b. and 219] as key 224 and relay 219 are assumed to be not yet operated'. A circuit may also be traced from negative battery through resistance 321, winding of relay 3|1, and contact 323D, to ground, energizing the winding of relay 3H. The path previously traced through contact 3|8s, armature of relay 3|8 and through contact 32821` to ground shunts the path through the winding of relay 3|?. Relay 3|? is a slow-to-release relay. Relay 3|1 does not release while relay armature 3|8 is in engagement with its contact 3|8s for normal spacing signals. However, if the armature of relay 3|8 remains in engagement with its contact 3|8s for a protracted period, relay 3|1 will release.

It will now be assumed that key 224 in Fig. 2 is operated. When relay 2|9 operates in response to the operation of key 224, contacts 2|9a.

vand 2|3e are opened. The path which extends from the tip of plug 20| to the repeater relays 222 and 223 was shown heretofore to extend through contacts 2|Sa and 2|9e. Contacts 2|9b and 2|'3f are closed. The teletypewriter transmission circuit of the operators position circuit, Fig. 3, is inserted in series between these points. This path will now be traced. The path extends through contact 2|9b, conductor 212, conductor 312, contact 303D, contacts SUIrZ and 30|?) in parallel, contact 3 9d, top winding of relay 3| 8, teletypewriter contacts 336, key Contact 343e, contacts 3021i and 302e in parallel, conductor 313 and conductor 213 to contact 2|9f. This inserts the transmission path of the operators position circuit in series with the main transmission path of Fig. l and Fig. 2. Negative battery through resistance 2| in Fig. 1 is connected to one end of this path. Positive battery through resistance 25| in Fig. 2 is connected to the other end of this path. The top or line winding of relay 3|8 Will be energized.` The effect of the energization of the top Winding of relay 3I8 is to actuate the armature of relay 3|8 to engage `vvith its contact 3|8m, as the effect of current in the top winding of relay 3|'8 preponderates over the effect or current in the bottom winding of relay 3|8. The effeet of the current in the bottom winding continues to tend to actuate the armature of relay 3|8 to engage with contact 3|8s.

As teletypewriter contacts ||6 are actuated at the subscribers station A in Fig. l, the armatureof relay 3|8 will be actuated between its marking and spacing contacts. Attention is again called to the fact that during the transmission of ordinary teletypewriter signals relay 3|1 Will remain operated. Since contact 3|1a is therefore open, ground is disconnected from one side of the teletypevvriter1 receiving magnet 335 so that the magnet may follow the received signals. These signals are impressed on the teletypewriter receiving magnet 335 in the following manner. With contact 3|1b closed instead of contact 3|1a, the circuit for the teletypewriter magnet may be traced from positive battery through resistance 3|2, winding of the teletypewriter receiving magnet 335, resistance 354 and contact 311D to the marking contact 3|8m of relay 3|8. When theiarmature ofrelay 3|8 is in engagement with its right-hand or spacing contact 3|3s, the circuit through the teletypewriter magnet 335 is open. When the armature of relay 3|8 engages with its left-hand or marking contacts 3 i 3m the circuit .is extended through the armature of relay `3|8 and through contact 328D to ground, energizing teletypewriter magnet 335. Thus in response to marking and spacing signals received by relay 3|8, the teletypewriter magnet 335 will be energized and deenergized. The necessary switching information to enable the operator at the central oiiice to complete or extend the call will be transmitted to the central station operatorin this manner.

Splitting feature in operator-s position circuit Keys 34| and 342 are provided so that, when both the answen'ng and calling ends of the cord perFig. 2 are connected to cooperating circuits, the operator may communicate With the `line connected to either the calling or answering end of the cord circuit as desired and prevent the signals from being transmitted through the opposite end which is meanwhile held in the marking condition to prevent the transmission of a false spacing signal. Operation of key 34| or 342 operates the corresponding relay 302 or 30| which splits the connection tothe desired direction and provides a termination for the holding cord. This will now be described in detail.

, If key 34| isoperated, a circuit may be traced from ground through contact 34|a and the winding of relay 302 tobattery, operating relay 302. When the transmitting path through the operators position circuit per Fig. 3 was traced it was shown to extend throughcontacts 302C and 302d in parallel. When relay 302 is operated these contacts are opened. In order to vhold the repeater in the cordr circuit `in the marking condition, negative battery is connected through resistance 3H and contact 302D to conductor 313. TThe negative battery connected through resistance 3| 'takes'the place of negative battery connected through resistance |2| in Fig. 1. Another circuit lis established which maybe traced from positive battery through resistance 3|2, Acontacti303d,` contact 302e, contact 343a andV contacts 33B to the top Windingof relay 3| 8. This" positive battery takes the place of positive battery connected through resistance 25| to the marking contact of relay 223.

With the circuit arranged in this fashion, the

top or line winding of relay 33 and teletypewriter transmitting contacts 336 are connected in series with the transmission path of the answering side of the cord which is connected to the transmission path of station A. .f Thusthe operator may communicate with the subscriber at station A. The signals will not be transmitted over the calling side of the cord, as the calling side of the cord will be maintained in the marking condition.

`When the calling side of the cord is connected to a cooperating circuit, in a manner to be described later, the operator may connect her position teletypewriter apparatus to the calling side of the `cord and communicate With a party connected thereto. i

In order to do this, the operator actuates key 342 rinstead of key 34|. This establishes a circuit which may be traced from ground through the contacts of key 342 and the winding of relay 30| to battery, operating relay 30|. i

When relay 30| is operated, contacts 30|b and 30|d are opened. Positive battery is connected through resistance 3|2, contact 303d, contact 30|c, contacti303b, conductor 312, conductor 212, contact 2I9b, resistance` 239 and contact 2|3d to the tip of plug 23|, rIhis positive battery takes the place of positive `battery heretofore supplied through resistance 25| and the marking contact of relay 223. The apparatus at the subscribers station in Fig. 1 is therefore held inthe marking condition. A circuit may also be traced from negative battery through resistance 3H, contact 30|e, contact 3|9cZ, top winding of relay 3|8, teletypewriter transmitting contacts 336,` key contacts 3430i, contacts 302C and 302d in parallel, conductor 313, conductor 213, contacts 2|8f, contacts 220b and 220e in parallel, bottom Winding of relay 222, armature and contact 223m of relay 223 and resistance 25| to positive battery. The negative battery supplied through resistance 3|| takes the place of negative battery formerly supplied through resistance |2| in Fig. l. The teletypewriter transmitting and receiving apparatus in the operators position circuit per Fig. 3 is connected to the calling side of the cord. Thus communication may be carried on exclusively through the calling end of the cord while the subscribers circuit per Fig. 1 is held to marking.

Recalll signal transmitting apparatus in operators position circuit The operators position circuit per Fig. 3 is arranged So that it may transmit a timed recall signal to a certain kind of trunk circuit, such as a ring-down trunk circuit, to which the cord circuit per Fig. 2 may at times be connected. In transmitting a, timed recall signal to such a trunk the transmission path through the operators position circuit is opened for a denite measured interval. In order to do this key 339 in Fig. 3 is operated. This establishes a circuit which may be traced from ground through the contacts of key 30, winding of relay 3|3 and resistance 329 to battery, operating relay 3|9. When relay 3|9 operates it locks through contact 3|9c to ground which takes the place of the ground formerly supplied through key 339. 'Ihe operation of relay 3|0 opens the transmission circuit through the operators position circuit at contact 3|9d. When contact 3|9a. closes ground interrupted at 60 times per minute is connected through contact 3|9a, the winding of the selector rotor magnet 322 and resistance 330 to battery, energizing rotor magnet 322. Rotor magnet 322 steps the switch arm of the single bank selector 32| successively around its contacts from No. 1 to No. 8 in eight seconds. When the switch arm of selector 32| reaches contact 8, the path to ground through the winding of relay 3 3l is shunted by direct ground through the selector brush arm and relay 3|9 releases. During the interval while the brush arm of selector 32| is moved from its normal idle position, off-normal contacts 3|6 are closed. When relay 3|9 releases a circuit is established from ground, through'contact 3|9b, contact Slt, winding oi' selector release magnet 323'and resistance 332 to battery, energizing magnet 323. When magnet 323 is energized it restores switch arm 32| to normal. Relay 3|!! has thus been energized and operated for a measured interval of eight seconds and then released. During the interval that relay 3 l 3 was operated, contact 3'l3d was open, which opened the transmission path through the operators position circuit. The opening of the transmission path resulted in a spacing signal of eight seconds duration being transmitted as a recall signal over any circuit connected to the answering and calling cord.

The operation of recall key 339 and splitting key 34| or 3132 enables a recall signal to be sent over a circuit connected to one or the other end of the cord while the opposite end is held to marking'if desired. A recall signal will be sent only over a trunk circuit. But, as shall be eX- plained below, either end'of the cord per Fig. 2 may Iat times be connected to a trunk circuit.

Busy, out of order, interference and practice indications in the position circuit As mentioned above, the circuits herein are arranged to provide busy indications for both ends of the cord circuit for Fig. 2. The man-v ner in which the position circuit cooperates to indicate the busy condition will now be explained.

Ii' any of the subscribers lines or trunk cir cuits are busy as explained above, battery is supplied to the sleeve of the corresponding jack. In order to make a. busy test with the answering cord the operator as explained above, touches the tip of plug to the sleeve of the jack. Similarly, the tip oi plug 2|! will be connected to the sleeve of one of the multiple line jacks. The tips of both plugs are connected in parallel to conf tact 23g. The circuit for plug 20| was traced from the tip of plug through Contact 2|3b to contact 2|3g. The circuit for plug 2|| was traced from the tip of plug 2H through contact 235D, contact Zilld and contact 2ND to contact 2| 9g. From contact Eidg the circuit extends through conductor 2M, conductor 3M and the Winding of relay 303 to ground, operating the armature of relay 333 to engage with its contact 308D. A circuit may then be traced from ground through contact 33319, armature of relay 308, resistance 339 and the filament of lamp 3|0 to battery, lighting lamp 3HE. This provides an indication that the tested line is busy. It should be pointed out that negative battery is supplied to the sleeve of the busy jack and that the armature of relay 308 is actuated to engage with contact 334e when negative battery is supplied to the left-hand termina/1 of the winding of relay 308.

It was pointed out above also that a lamp was lighted in the position circuit to indicate that two cords are connected simultaneously to the same subscribers line circuit. This lamp is lighted in the operators position circuit connected to the interfering rcord only. It was pointed out that relay 203 was operated in the interfering cord only. This establishes a circuit from negative battery through resistance 232, contact 203i; and contact 2|9g. Negative battery connected to contact 2l3g, as has been pointed out, results in the operation of the armature of relay 308 in the operators position circuit per Fig. 3 to engage with its contact 308D. This in turn lights lamp 3 E 0 as an indication of the interfering condition. Thus the lighting of lamp 3|0 may indicatev either a busy condition or a cord interfering condition.

Oi course a line should be tested before the plug of a cord is completely inserted in a jack. If a line is busy the operator will observe the lighted lamp. If she fails to test for busy, however, and inserts her plug such .as 20| in a jack, to a multiple appearance of which another cord is already connected, lamp 3|0 will be lighted in the interfering cord and the operator will remove the interfering cord lf a line when tested is busy due to being connected up for practice, a positive potential will be present on the sleeve of the line and relay 305 which is connected in parallel with relay 308 over a circuit which may be traced, through the winding of relay 304 and the Winding of relay 305 in series to ground, will operate. The current for this condition is not sulcient to operate relay 30d. The armature of relay 305 is actuated so as to engage with contact 30522. A circuit may then be traced from ground through contact 305b and the armature of relay 305, winding of relay 305, contact 301th and resistance 3|3 to battery, operating relay 306. The operation of relay 306 establishes a circuit from ground through contact 306e, winding of buzzer 301, filament of lamp SI5 and power supply 3|4 to ground, lighting lamp 3|5 and operating buzzer 307. The simultaneous operation of buzzer 301 and lamp 3|5 indicates to the operator that she has tested a circuit which is connected up for practice and she will plug in notwithstanding the indication to seize the line. i

If a line when tested is out of order, a positive potential will be present on the sleeve of greater magnitude than in the case or" a circuit which is being used for practice. Under this condition both relays 3M and 305 will operate. The armature of relay 305 will be actuated so as to engage with contact 3051). A circuit may now be traced from battery through the nlament of lamp 3|0, resistance 309, contact 301m, winding of relay 306 and armature and contact 305D of relay 305 to ground. Lamp 3|0 Awill light and relay 336 will operate. The operation of relay v306 will establish a circuit from ground through contact 306e., buzzer 307,'filament of lamp 3 l 5 and power source 3|4 to ground. Signals provided under these conditions will indicate the out-of-order condition.

- Disconnect circuit It is pointed out that the operators position circuit per Fig, 3, when connected to the cord circuit per Fig. 2, functions with'a number of different kinds of trunk circuits. Supervisory signals are transmitted over these dilierent kinds of trunk circuits in different manners. Withcertain connecting trunks the supervisory signals assassin are 'transmitted fon a 'timed basis. Disconnect signals vover certain trunks `are open signals of ten Asecon-ds duration. `In transmitting such vsignalsthe 'calling 'end 'of the cord is open for a periodof ten seconds and then reclosed. A disconnect 'circuit shown in the lower right-hand corner of Figu is provided in order to cooperate with relays in the `cord circuit to perform this function. This `will now be described `in detail.

Although the operators `position circuit per Fig. 3 is equipped individually with selector'apparatus to provide a recall signal, the disconnect apparatus which transmits 1a timed disconnect signal is provided only 'once per 'position and is connected to each of the cord circuits kat the i positions as required by the operation of a key in the cord.

First `the transmission 'path vthrough vthe calling end ofthe cord circuit per Fig. 2 will be traced and then the manner in which the disconnect circuit in Fig. 3 functions to open this path for an interval of approximately ten seconds to transmit `a disconnect signal over certain kinds of trunks will be described.

When plug 21 I is connected to a trunk,` ground over the sleeve of lthe trunk i's connected throughI 'the sleeve of plug 2H to battery through the winding of 'relay 2H and resistance 263 in parallel, operating relay 2H. This closes contact 2nd. The circuit for the transmission path f through the calling end of the cord may now be traced from the tip or top conductor of calling plug 2| I through contact`235b, contact 20811, contact 2| 1d, contact 2`l8a, resistance 243, bottom winding of relay 223, armature and right-hand a or marking contact 222m of relay 222 and resistance 250 to positive battery. It is to be understood, in the cooperating trunk thel tip conductor extends to negative battery through a telegraph repeater for this condition. x

In order to connect the disconnect circuit and transmit a disconnect signal, the operator will operate key 34. A circuit may now be traced Sao from ground through contact 2340i, left-hand winding of relay 218, conductor 211, conductor 311, and contact 346i! to battery operating relay 218. The operation o'frelay 2 I8 opens the transmission paththrough the calling end oivv the cord by opening Contact 2|8a. When relay 218 oper- 1 ates it locks over a path which may be traced from battery through the right-hand winding of relay 2l'8, contact 2l8c, conductor 21B, conductor 318, winding of relay 346 and contact 3481) to ground. Relay 346 operates.

The operation of relay 346 provides an operating circuit for the disconnect signal, selector rotor magnet 352. This circuit maybe traced from battery through resistance 33|, winding of rotor magnet 352, contact 346e and interrupter 360 to ground. The interrupter provides ground interrupter by open circuits at 60 times per minute. Rotor magnet 352 drives the brushes of the selector banks 344 and 353 off their normal posirvta tions of rest as indicated and then from terminal to terminal until the brushes of each bank reach terminal l0. During the interval that relay 346 is operated, a lamp such as lamp 349. will be lighted at the operators position as an indication that the disconnect circuit is in use. The lamp circuit may be traced from battery through contact 346D and through the filaments of lamps 349 and resistances 350 in parallel to ground.

When the brush of selector bank 344 reaches terminal I0, a circuit is established from ground through the brush and terminal I0 of bank 344,

`W'in'di'ngoi relay 345 and contact 3461) to battery operatin'g'ielayi' When relay 345i`s operated, it is held operated, over a locking circuit through Tits fc'on'ta'ct `3451), by which ground is Asupplied `to -theet'op terminal fof vthe 'Winding of relay 345 to take theplac'e of ground formerly `supplied thereto through the brush and contact lil of selector bank 344.

If an operator at another position fdisregards the flamp `such as 349 at her position, indicating that the disconnect circuit is busy, and attempts to use the disconnect circuit by operatinga key corresponding to ke'y 234 in a cord at her position, the 'disconnect circuit 'will not Abe connected tothe new cord; as battery is disconnected 'from the Acircuit to the' new `cord by the operation of vrela'y 346 in the single disconnect circuit. The disconnect circuit will therefore not be available 'for use @by 'any otherfoperator :at 'another posi- `tion until relay 346 in 'the disconnect 'circuit r'eleases. Whilerelay 345 is operated, a 'circuit is 'provided for the energiza'tio'n of the release inagnet 35|"of the selector. This circuit Ymay be traced from ground through 'contact 345e, con- 'tact -341a of the selector A"oit-normal i'sprir'igs windingof release magnet 35| and :resistance 333 to battery. It `should be y'pointed out that whilel the brushes "of the `selector are moved oi their id-1e positions, a's shown in'Fi`g.` 3, Vsprings 34M and 341D are rclosed 'by the iselector mechanism in a well-known manner. During the next interval that thepath through theinterrupter 360 to `ground is open, at which time the'selector rotor magnet 352 is 'deenergize'd, the energization of release 'Inagnet35l will'beeffective to restore the-brushes of selector bank 34'4 and 353 'to their normal` idle position 'as shown in Fig. 3, As 'soon as the circuit to ground through the interrupter fis again closed, 4the rotary magnet 352 'is once more energized and brushes of selector banks 344 and '-353 are again stepped. This time, however. the brushes Astep but one position only. It is pointed out that when 'the brush 'associated with ,selector bank 353 r'st passedover'its associated terminal- I, the path to battery through the right-hand winding of re'lay 348 and' contact 34511 'was not available, 'as "relay 345 4was not operated. When the brush of selector bank 333 engages terminali the 'second' time, however, a path is `establishedwhich 'may be 'traced from groundA through the brush andterminal Il 'of selector bankV 353, right-hand winding "'o'f relay 348 andeontact 34'5ato battery, 'energizing and operating relay 348.` When "relay 348 operates it locks 'over a path 'which may be traced from battery throughthe" lett-hand Winding ofrelay 348,'contact 348i; 'and Contact 345c`to ground. The operation of relay 348 opens the 'path to ground through contact I343i) over which relay "Zl inFig. 2 Was'held operated. ssoon asthe next open period of the interrupter occurs, ground will be removed from the path through the winding of relay 34e andthe winding of relay 2|`8 zin the cord circuit and relays 346 and 218 lwill release. The release of relay 218 inthe cord reestablishes the transmission path through the calling end ofthe cord, whichhas `been open for approximately ten seconds. The vrelease of relay 346 also opens the path overwhich relay 345 hasbeen held operatedat contact 34617 and relay 345 releases. The release of relay 345,` by openingA contact 345C opens the holding path for lrelay `348 and relay 348 releases'.l As soon as ground was disconnected by interrupter 360 from the path throughv rotor magnet- 352 and before relay 345 released, the winding :of release magnet 35| was energized andv it was effective to restore the two brushes of selector banks 344 and 353 to normal. In order to eliminate the possibility of the release of relay 345 before the release magnet 35| has restored the selector brushes to normal, relay 345 is maintained operated by battery from the ofi-normal spring contact 341D until the selectorbrushes have been returned to normal.

K Toll ringing from operators position circuit The circuits herein are arranged so that a ringing signal may be transmitted from the position circuit per Fig. 3 through thecord circuit per Fig. 2 over certain of the rtrunks tov which calling plug'2 may at times be connected. These particular -cooperating trunks are varranged so'that in response to the opening of the transmission pa'th of the position circuit for a definite interval when it is connected in series with the repeater relays in the cord a ringing signal will be registered at the distant end of the trunk. While the calling end of the cord and position circuit is opened the answering end of the cord and position circuit will be closed to vpositive battery to hold the circuit associated with the answering end of the cord inthe marking condition.

Iny order -to perform the above functions the armature of key 343 is actuated so as to close contact 34312. This opens contact'343a. This opens the circuit which may be traced from open contact 3||3av through contacts 302e and 3|l2d in parallel, conductor 313, conductor 213, contact 2| Bf, contact 220b1and'cont'act 220e in parallel, bottom winding of relay 222, armature of relay 223, Vcontacts 223mand resistance 25| to positive battery. As a'result of the opening of contact 343a the bottom winding of relay 1222 will be deenergized. 'I'he armature of relay 2212 will' be operated to engage with its spacing contact 222s and a spacing signal will be transmitted over the transmission path associated with the calling end of the cord to the connected toll trunk circuit as a ringing signal. While the armature of key 343 is inv engagement with contact 343!) a circuit may be traced from positive battery through resistance 3|2, contactf34lb, contact` 343D, teletypewriter transmitting contacts 336. top winding of relay 3|8, contact 3|9d. contacts 30H7 and 3|l|d in parallel, contact 30373,' con- `ductor 312,` conductorv 212. contact `2`| Slip-resistance 239 and contact 2| 3d to the tip of plug 20|. From this point the circuit has been traced around the subscribers loop and back to negativebattery through vresistance |2|. This holds this circuit in the marking condition while the ringing signal is being transmitted over the calling end of the cord through `the connected toll trunk circuit.

Under certain circumstances, as shall. be eX- plained, the answering vend of the cord'circuit per Fig. 2` may be Yconnected to a toll trunk. Under such circumstances it may be desired to transmit a toll callsignal on the answering cord. In order to do.this..splittin`g key 34| is first operated andr then toll ringing key 343is actuated so as to close ,contact .34317. The operation of .key 34| establishes a circuit fromvground through contactA 34|aand the winding of relay 302 to Vbattery operating relay 302. As has been shown above, when relay 302 is operated the calling cord transmission path is held to marking by negative vbattery `connected through resistance 3| l, contact SMIL-conductor 313, conductor 213, contact 2| 3f; contact' 22012, bottom winding 'of relay 222, contact. 223m and resistance 25| to positive battery. Operation of key 34| and relay 302 also connects positive battery through resistance 3|2 and contact 332e tothe answering end of the cord but the operation of toll ringing key 343 will under this condition, open the op' erators position circuit transmission path connected in series. with the answering cord. An openV signal is therefore transmitted over the answering endof the cord and-the toll trunk connected thereto as a ringing signal.'

Monitoring Qn operators position circuits .from ground, through vtheV sleeve of plug `351,

sleeve of jacky 334 and throughY the winding of relay 320 to battery. A circuit may be traced from the left-hand. or marking contact 3|8m through contact 3|1b and-contactl 320I) to the tip of jack 334. A circuit may also be vtraced from positive battery through resistance SI12, resistance 356 and contact 32M to the ring conductor of jack 334. The tip and ring conductors of plug 351insertedin vjack 334 connect to the opposite terminals of teletypewriter receiving magnet 35S-in the supervisors `monitoring circuit. This magnet is, therefore, connected in parallel with magnet .335 in the operators position circuit. When the armature of relay 3| 8 lis operated so to engage with its marking contact 3|8m, ground through key contacts 328D and the armature of relay 3||i-will be connected to this circuit to energize the teletypewriter magnet in the supervisors monitoringfcircuit simultaneously with the energization of the teletypewriter receiving magnet 335 in the position circuit. As the armature of relay 3|8 follows the operation of teletypewriter transmitting contacts 336 all signals received in the operators position circuit per Fig. 3 and transmitted from the operators position circuit per'Fig. 3 will be registered in the supervisor-s monitoring circuit. v

Extending call from cord circuit over automatic signaling intertoll trunk The reader is reminded that the central oiiice at whichthe call from subscribers station A originatesv is called oice I. 'I'he distant central oiiice through which the call is tobe extended is called office 2.

Figs. 4, 5, 6 and 7 arranged as indicated in Fig. 9 form an automatic signaling intertoll trunk. The trunk terminating circuit, per Fig. 4, and the repeater circuit, per Fig. 5, are located at office The repeater circuit, rper Fig. 6, and the trunk terminating circuit, per Fig. 7, are at oice 2. There are also other kinds ofv trunks, such as ringdown trunks. terminated at the operators position in oiiice I. The cord circuit, per Fig. 2 and the position circuit, per Fig. 3, as mentioned above, are arranged to function with all of the Itrunks terminated at the operators position.

In the following description the manner in which the Vcall incoming from station A in Fig.

1 is extended from oice I to oflce 2 through the cord circuit, per 2, over an automatic signaling intertoll trunk circuit per Figs. 4, 5, 6 and 7 will be described rst in a general way to describe the physical arrangement of the units and then in detail.

The jacks 401 and 402 shown at the upperl left of Fig. 4 together with their associated lamps 403, 404, 4115 and 406 are located in a teletypewriter switchboard at office I. The jack 402 and its associated lamps 405 and 40B`will appear at one operators position. The jack 401 and its associated lamps 403 and 404 will appear at another operators position, providing what is known as a multiple appearance of jack 402 and lamps 405 and 406. The leads extending toward the lefthand margin of Fig. 4 indicate that the jacks and lamps appear also at otheroperators positions.

At the right-hand end of Fig. 4 two jacks 401 and 408 are shown. These jacks appear at a telegraph test board in oice I. After passing through the telegraph test board the two transmission conductorsAIZ and 413 extend by means of` conductors 512 and 513 through a telegraph repeater shown in Fig. 5. The telegraph repeater, per Fig. 5, is located at office 1. From the telegraph repeater per Fig. 5, two transmission conductors 501 and 508 extend from office Ito office 2. They connect to conductors 601 and 608, respectively, at oice 2.. At oice 2 the two conductors 601 and 600 connect to another telegraph repeater shown in Fig. 6. The telegraph repeater is connected vby two conductors 812 and S13 to conductors 112 and 113 in Fig. 7 which extend to a telegraph test board at office 2. Jacks 101 and 108 shown at the left of Fig. '1 appear at the telegraph test board at office 2. telegraph test board at oiiice 2 the path con-` tinues through the trunk terminating equipment, per Fig. 7 to the jacks and lamps shown at the upper right of Fig. 7. V'I'hese jacks and lamps are arranged in the switchboard at office 2 in a manner corresponding to that described for the jacks at the upper left of Fig. 4 in the switchboard at office I Key 224 in Fig. 2 will remain operated to its alternate position and Fig. 3 will remain connected to Fig. 2. l

Please refer now to Figs. 4, 5. 6" and 7. These circuits are shown with the armatures of all of the various polar relays in `engagement with their spacing contacts. When the trunk circuit is idle no current flows in any of the windings `of the polar relays shown in Fig. 4 and Fig.y '1 except in the top winding of relay 418 in Fig. 4 and in the top winding of relay 118 in Fig. 7. The armatures of these two relays are actuated to engage their spacing contacts as shown. The armatures of relays 415, 416 and 41'! of Fig. 4 and 115, 116 and 111 in Fig. 7 are assumed to be in engagement with their spacing contacts, as shown. before their windings are energized. The armatures of relays 501 and 502 in Fig. 5, 1501 and. 602 in Fig. 6 are all operated to engage their spacing contacts. No current flows in the top windings of relays 50| and 001 and their arma tures are actuated to engage their spacing conn tacts by the effect of current flowing through their bottom windings. The armatures of relays 502 and 602 are actuated to engage their spacing contacts by the e-iiect of current supplied from the spacing contacts of relays 501 and 601, respe-ctively. None of the vacuuml tubes in. Figs. Lland 7 are activated. Relay 418, when its armature From the is on its spacing contact, will keep condenser 461 discharged by connecting ground to its top contactthrough contact 424a. Similarly, relay '118 will keep condenser '161 discharged by connecting ground to its top contact through contacts '12411.

After testing jack 402, in the manner described above, plug 211 will be inserted in jack 402. This establishes a circuit from ground through the winding of relay 419 in Fig. 4, Sleeve of jack 4112 and the sleeve of plug 211 to negative battery through the winding of relay 211 and resistance 203 in parallel. Relays 419 and 211 operate. A circuit is also established from ground through resistance 400, ring of jack 402, ring of plug 21,1 and the winding of relay 21B to battery. Relay 216 does not operate at this time as resistance 400 is of too high a value. The operation of relay 21.I establishes a circuit from battery through contact 211e, resistance 252 and the winding of relay 200 to ground operating relay 200. The operation of relay 211 also closes the transmission circuit of the calling end of the cord at contact 21'1d.. The operation of relay 209 establishes a circuitfrom ground through contact 209e and the right-hand winding of relay 206 to battery operating relay 2116. The operation of relays 209 and 205 performs no useful function at this time.

It is pointed out that as relay 215 is not operated supervisory lamp 231 remains unlighted at this time.

Refer now to Fig. 4. The operation of relay 410 establishes a circuit which may be traced from ground through contact 4101.1 and the winding of relay 420 to battery operating relay 4211. The operation of relay 450 also establishes a path from ground through contact 41911. and the winding of relay 414 to battery operating relay 414. The operation of relay 420 establishes a path from ground through contact 420g, resistance 430,V bottom winding of relay 415, bottom winding of relay M6 to the armature of relay 411.

The operation of relay 420 also established a circuit which may be traced from battery through resistance 444, bottom winding of relay 411, contact 48M, resistance 491 and contact 420k. to ground. The effect of current ilowing in this path actuates the armature of relay 411 to the right to engage it with its marking contact 411m, A. circuit may now be traced from negative bat-v tery through resistance 443, contact 411m, armature of relay 411, top winding of relay 416, top winding of relay 415, resistance 431, resistance 435, contact 414g, tip of jack 402, tip of plug 211, contact 235h, contact 20M, contact 211d, contact 2180., resistance 243, bottom winding of relay 223, armature of relay222, contact 222m and resistance 250 to positive battery. Full line current will flow through the top windings of relays 415 and 415. Theeiect of this current actuates the armatures of relays 415 and 41S to the righ-t to engage their respective marking contacts 415m and 410m, as the effect of full line current in the top windings of these relays is dominant over the effect of current in the bottom or biasing windings of these relays which is tending to actuate the armatures of these relays toward the left to engage their respective spacing contacts 415s and 415s. Relay 414 is locked over a path from battery through the winding of relay 414, contact 414e and contact 42041 to ground. The opera` tion of relay 420 also establishes a path from ground through contact 42e@ and the winding of `relay 421 to battery Operating relay 4,21.. The operation of relays 420 and 421 also provides.V a

charging path for condenser 465 as follows: When relay 421` operated ground was connected through contact 421e and resistance 466 to the bottom terminal of relay 465. A circuit may also be traced from battery through resistance 415 to parallel branches. One branch extends through resistance 452 and contact 425e. Ihe other extends through resistance 466. The branches join' and the circuit continues through contact 426e to the top terminal of condenser 465. Condenser 465 will be charged. The operation of relay 421 also established a path for the lighting of the laments of vacuum tubes 43|, 432, 433 and 434. This path may be traced from battery through resistance 415, resistances 413 and 414 in parallel, filament of tube 434, resistance 412, filament of tube 433, filament of tube 432, resistance 461, filament of tube 43|, resistance 411 and contact 421e to ground. The operation of relay 421 also lights each of the busy lamps 465, 463, etc., associated with the jack multiple circuit in the various operators positions in the switchboard as a warning that the circuit is in use so that no operator at the other positions Where the multiple jacks appear will attempt to establish a connection through the multiple jacks. The lamp circuit may be traced from ground through the lament of lamps 465, 463, etc., in parallel and contact 421a. to an alterhating current supply circuit 492. The operation of relay 421 also establishes a circuit which may be' traced from battery through resistance 456 and contact 421b to the sleeve of jack 466. Jack 466 is a test jack located in the toll test board at oiiice Battery connected to the sleeve of the'jack serves as a busy test battery supply. It is impressed on the circuit whenever relay 421 is operated so that the test man at the telegraph test board Will not take over the circuit for test when the circuit is in use. As long as relay 466 remains unoperated current through the bottom winding of relay 4|? will maintain the armature of relay 4|? on its marking contact. The transmission circuit interconnecting the cord per Fig. 2 and Fig.` 4 will thus be maintained in the marking condition.

ADuring the interval while the laments of the tubes are heating, positive battery has been connected through resistance 415, resistance 455, and contact 426a to a parallel circuit. One branch connects to the left-hand terminal of condenser 416, the right-hand terminal of which is connected through resistance 41| to ground. The other branch extends through resistance 468 to the grid of tube 433. Condenser 416 has become charged. As soon as the filaments of the tubes are heated, tube 433 becomes conductive. A circuit is then established from positive battery through resistance 415, winding of relay 436, anode of tube 433, cathode of tube 433 to ground Athrough contact 421e operating relay 436.. The operation of relay 436 establishes a path from ground through contact 4360l and the winding of relay 42| to battery operating relay 42|. The operation of relay 42| establishes a path from battery through the Winding of relay 426, contact 42| a and contact 4|6c to ground operating relay 426. When relay 426 operates it locks over a circuit from battery through the Winding of relay 426, contact 426C and contact 4|9c to ground. The operation of relay 426 establishes a circuit from ground through contact 4|5m, contact 426|) and resistance 466 to the grid of tube 433. Tube 433 becomes non-conductive. Relay 436 releases. The release of relay 436 in turn releases relay 42|. During this time condenser 465 will have become charged to full potential. Tube 43|, the grid of which is connected to the top terminal of condenser 465 through resistance 464, then becomes conductive. The grid of tube 432 is connected to the anode of tube 43| and when tube 43| becomes conductive tube 432 is maintained non-conductive.l

A circuit may now be traced from negative battery through resistance 446, contact 4|6m, resistance 44|, contact 42|c, Contact 42611, contact 46119, conductor`4|3 into Fig. 5 Where it connects to conductor 5|3 and the circuit continues through resistance 563, top'winding of relay 56| and resistance 566 to positive battery. Full line current ilows through'the top winding of relay 56| andlitis eiTective to actuate the armature of relay 56| to engage with its marking contact 56|m as the effect of the line current dominates over the eiect of'biasing current owing from positive battery through resistance 566, bottom Winding of relay 56| and resistance 564 to ground tending to actuate the armature of relay 56| to- Wardits spacing contact 56|s. A circuit may be traced from negative battery through contact 56|m and conductor 561 into Fig. 6 Where it connects tocondu'ctor 661 and the circuit continues through the Winding of relay 662 to ground. The armature'v of relay 662 is actuated to engage with its marking contact 662m. A circuit may be traced from positive battery through contact 662m, resistance 665 and conductor 6|2 into Fig. 7 where it connects to conductor 1|2 and the circuit extends through contact 161e, resistance 156, bottom Winding of relay 1|8, bottom Winding of relay 1|1 and resistance 144 to negative battery operating the armature of relays 1|1 and 1|8 to the left to engage their marking contacts. When the armature of relay 1|8 disengages from its spacing contact 158s it permits condenser 16| to start charging over a'circuit corresponding to that traced for "condenser 46| in Fig. 4. When the armature of relay 1|8 engages with its marking contact 1| 8m, a circuit is established from ground through contact 1|8m, contact 12617, contact 1|4d and the winding of relay 121 to battery operating relay 121. The operation of relay 121 will establish a circuit to light the filaments of tubes 13|, 132, 133 and 134 in the same manner as described vfor Fig. 4. The operation of relay 121 will also supply negative battery through resistance 156 and contact 12119 to the sleeve of jack 166 as a busy potential. The operation of relay 121 will apply negative battery through resistance 158 and Contact 121d to the sleeves of jacks 16|, 162, etc., as a busy potential. The operation of relay 121 will connect an alternating current supply circuit 162 through contact 121a and the laments of busy lamps 163, 165, etc. to ground lighting the busy lamps. When the laments of the vacuum tubes are energized tube 133 is activated and relay 136 is operated as heretofore described. This `in turn operates relay 12| which has also been described.

When the marking signal is in excess of onehalf second condenser 16| will be charged suiciently to permit tube 132 to function as the positive potential impressed on its top terminal will be impressed through resistance 163 on the grid oi" tube 132. Relay 126 will operatel over a cir.- cuit from positive battery through resistance 115, Winding of relay 128,an0de of tube 132, cathode of tube 132 to ground through contact 121C. This in turn will establish a circuit through Contact 128a and the Winding of relay 124 to battery operating relay 124.

The operation of relay 124 will open the circuit from the spacing contact of relay 1I8 at contact 124a so that tube 132 will remain conductive. The operation of relay 1.24 will establish a circuit from ground through contact 124C, contact 1I4b and the winding of relay 123 to battery operating relay 123. The closing of contact 124e will establish a circuit from battery through resistance 15|, contact 124e and the winding of relay 125 to ground operating relay 125. When relay 125 operates it will lock over a path from ground through the winding of relay 125, contact 125e and resistance 15| to battery. The operation of relay 125 establishes a circuit from ground through contact 1251i and the Winding of relay 120 to battery operating relay 1.20. The operation of relay 125 also establishes a circuit from ground through contact 125i and the Winding of relay 180 to battery operating relay 180. The operation of relay 120 will close the biasingr circuits of relays 1|5, 1|6 and 1|1. The circuit for relays 1|5 and 1I6 extends from ground through contact 120g, resistance 138 and the bottom windings of relays 1|5 and 1I6 to the armature of relay 1.I1,` which is in engagement with contact 1|1m. The circuit for relay 1|1 extends from the armature of relay 1I6, which engages its spacing contact, through the top winding of relay 1| 1, contact 180o, resistance 19| and contact 12071. The operation of relay 120 will hold relay 121 operated over a path from battery through the winding of relay 121 and contact 120e to ground. The operation of relay 123 will establish a circuit from ground through contact 122d and contact 123a to the night alarm circuit operating the night alarm circuit. rPhe operation of relay 123 also establishes a circuit from battery through contact 1231i, contact 122e and thelaments of lamps 104, 106, etc. in parallel to ground lighting the lamps as a signal that a call is incoming from oflice The operation of relay 123 will connect battery through resistance 149 and contact 123e to the tip of jack 108. When relay 180 operates it locks over a circuit from battery through the winding of relay 180, contact 180D and contact 120a to ground. The operation of relay 1.80 prepares the lead extending from the ring of jacks 102, etc., which connects to resistance 190 in parallel with contact 180a for future supervisory conditions.

Abandoned call If the incoming call is abandoned before the operator at office 2 answers, by removing plug 2| I from jack |02, the transmitting path from oiiice I to office 2 is returned to spacing. When the armature of relay 1I8 breaks from its contact 1I8m ground is disconnected from the `top terminal of condenser 165. The circuit may be traced from the top terminal of condenser 165 through contact 120e to contact 1I8m. This permits condenser 165 to charge over a circuit which may be traced from positive battery through resistance 115, resistance 160 and contact 120d to the top terminal of condenser 165. Afterl the condenser has charged for one-third second tube 13| will become conducting and carry the grid of tube 132 to a potential which is negative with respect to its filament so as to make tube 132 non-conducting. Relay 128 Will release. This releases relay 124. The release of relay 124 in turn releases relay 123. The release of relay 123 extinguishes line lamps 104, 106, etc. at the switchboard. Two-thirds of a second after tube 13| has become conducting tube 134 will become conducting due to the increased potential of condenser 165 which is impressed on the grid of tube 134. This establishes a path from positive battery through resistance 115, left-hand winding of relay 129, anode of tube 1.34, and the cathode of tube 134 which extends to ground through contact 121C operating relay 129. The operation of relay 129 will establish a circuit from battery through resistance 15| and contact 125e to parallel branches. One branch extends through the winding of relay 125 to ground. The other branch extends through contact 12512 and contact 129a to ground. This applies direct ground to the top terminal of the Winding of relay 125 shunting the path through the winding of relay 125. Relay 125 releases. The release of relay 125 in turn releases relay 120 by opening contact 1.2503. The release of relay 120 establishes a path from the top terminal of condenser through contact 120d to ground through contact 1I4f discharging condenser 165. This causes tube 134 to become non-conductive. This in turn releases relay 129. The release of relay 129 will in turn release relay 160. The release of relay will release relay 121 restoring the circuit at oflice 2 to normal.

Operator at oice 2 answers call incoming over trunk If the call is not abandoned the operator at ofce 2 will respond tothe lighted line lamp at her position by connecting the answering `plug 20| of a cord circuit such as Fig. 2. in her position at olce 2 to the trunk line jack at her position. It will be assumed that plug 20| is connected to jack 102. The cord circuit at cnice 2 .is identical with that at office I. The tip ring and sleeve conductors of plug 20| are connected to the tip ring and sleeve conductors of jack 102. A circuit is established from ground through high resistance 190, ring of jack 102, ring of plug 20|, winding of relay 202, winding of relay 2|2 to battery operating relay 202. Relay 2|2 does not operate due to the high Value of resistance 190. A circuit is established also which extends from ground in Fig. '7 through the Winding of relay 1I9, sleeve of jack 102, sleeve of plug 20|, contact 2681), lefthand winding of relay 205 and the winding of relay 204 to battery. Relays 1|9, 205 and204 will operate. In the cord per Fig. 2, the operation of relay 204 will operate relay 2|3. This in turn will operate relay 22|. The operation of relay 22| will energize the biasing and holding circuits of relays 22-2 and 223. Key 224 and relay 2|9 Will be operated. These operations are the same as explained for ofce I. The operation of relay 1|9 in Fig. 7 will establish a circuit from ground through contact 1|9c, contact 12 la and the Winding of relay 126 operating relay 126. The loperation of relay 1|9 also establishes a circuit from ground through contact 1 |9a and the Winding of relay 1I4 to battery operating relay 1I4. When relay 1 I 4 operates it locks over a path from battery through the winding of relay 1I4, contact 1|4c and contact 120:1 to ground. The operation of relay 1I4 releases relay 123 by opening contact 1|4b. The operation of relay 1 I4 also changes the charging path of condenser 16| from a highl resistance to a low resistance path by closing contact 1I4a which short-circuits resistance 135. The operation of relay 1 |4 also closes the transmission path of the tip conductor at contact 1|4g. This path may be traced from negative battery through 

